Room-temperature photon-counting receiver scheme for cosmic microwave background polarization measurements

In this paper, a proof-of-concept sub-THz detector for its use in radio telescopes is presented. The detector is intended to work at room-temperature and to be suitable for cosmic microwave background B-mode polarization measurements, so a high sensitivity photon-countig receiver is required. The proposed detector is a practical arrangement of several receivers, each one working on the principle of nonlinear up-conversion of the sub-THz signal into the optical domain by using a lithium niobate (LiNbO3) whispering-gallery mode (WGM) resonator. This concept of receiver has theoretically shown capabilities towards photon counting. The system is evaluated and is shown to be suitable for cosmic microwave background polarization measurements.